Heating and cooling appliances are in wide use in buildings and in residential and/or commercial industry. Examples of such heating and cooling devices include air conditioning units, heat pumps, gas fired boilers, gas fired furnaces, circulating solar water heaters, and a wide variety of other equipment that is used to provide heating or cooling to an atmosphere such as for example a building atmosphere, or to a process fluid in industry. Other types of appliances are also used to provide heating or cooling to environmental or industrial systems. For example, a storage room such as a refrigerated cold box requires cooling to be applied. Also, many industrial processes require the heating or cooling of a fluid. For example, in an industrial process where a vessel is heat jacketed or cold jacketed, the fluid will be heated or cooled using some form of heating device or chilling device.
In most of systems, it is typical to have an on/off type thermostat device that senses the temperature of the environment compared to a predetermined desired temperature, and turns the heating and/or cooling device or other appliance on or off to add heating or cooling energy inputs to the environment. A wide variety of simple and programmable thermostats is known, which turn the system on or off when the deviation from the desired temperature exceeds a predetermined threshold.
The above described systems suffer from drawbacks however. Because the heating and cooling requirements of many all environments will vary from time-to-time, the heating or cooling appliance is generally over-designed so that when necessary it can overcome maximum loads. Consequently, the entire device is cycled on and off, therefore sometimes causing a number of cycles, which may be somewhat energy inefficient. One solution to this problem is to reduce the design limits of the system, however in some instances then it will not be able to meet peak demand loads. Another solution is to over-design the system to meet peak demand loads, which causes the system to become more expensive and as mentioned above, to go through cycles which may have an inefficient start-up and shut-down times. Further, such a cycling type of input may in some instances lead to swings in the temperature of the environment, which may be acceptable in some environments, but may not be acceptable in environments where it is desired to hold the temperature in an extremely even condition.
Also, use of a single large system can preclude the use of some systems such as solar water heating, which may be sometimes but not always available due to the weather.
In view of the foregoing, there is a need in the art for a system for control of appliances such as heating and cooling devices which can respond to changes in heating or cooling load in a desirable manner, while also reducing the total cost of the system and/or improving the energy efficiency of the system.